What I have said will enable us to explain how exhalation is effected.
It is by the same principle as that to which we have before referred;
it is that which will serve for the explanation of secretions,
absorptions, &c. There is between the elements which form each exhaled
fluid and the organic sensibility of each kind of exhalants, such a
relation, that these elements alone can be admitted by the vessels
which reject the others, so long as there is no change in their kind of
sensibility. The general capillary system appears to be the reservoir,
in which, as I have said, the blood is elaborated; it is there that
the red blood becomes black; it is there at the same time that its
different elements are separated, combine anew, and during these
changes disengage caloric. It is after these changes, these different
transformations, that each exhalant takes, chooses as it were the
portions with which its sensibility is in relation, and leaves the
others.
It follows hence as a very simple consequence, that whenever the
organic sensibility of the system in which exhalation takes place
is altered in any manner, exhalation should also immediately vary;
and this in fact always happens. There is never any derangement in
the exhalations, without a preceding one in the sensibility of the
exhalants. Take for example the different injuries of transpiration;
you will see that cold, heat, dryness, moisture, frictions, &c. always
exert their influence upon the cutaneous sensibility, and that the
derangements of the exhalation are consequent to them.
The organic sensibility of the exhalants, like that of every other
part, may be disordered in different ways, 1st, by a direct stimulant,
as when cold contracts the skin, when a very cold fluid acts upon
the stomach, &c.; 2d, by sympathies, as when the acute affection of
the fibrous and muscular organs produces sweat in rheumatism; 3d,
oftentimes without our being able to say how, a derangement takes place
in the vital forces of a part; of this inflammation presents frequent
examples. I do not allude here to that which takes place from the
contiguity of organs, &c. &c.
It follows from this, that when exhalation is preternaturally increased
or diminished, the sensibility of the exhalants is always modified in
one of the three preceding ways.
Now if we reflect upon the different kinds of exhalants, we shall see
that there are no others except the cutaneous and the mucous which are
exposed to the immediate application of stimuli, since they alone are
in relation with external bodies. Besides the two modes of alteration
of sensibility that they share with others, they have moreover this.
It is not then astonishing, that their exhalations, especially
the cutaneous, exhibit such numerous varieties, that the skin is
continually found varying between the greatest dryness and the most
copious sweat.
The sympathetic exhalations are extremely numerous. I shall not give
examples of them here; many may be found in the sympathies of the
dermoid, serous, mucous systems, &c. I would only observe that authors
have not sufficiently distinguished this kind of exhalations from
the others; nor has sufficient attention been paid to sympathetic
secretions.
The exhalations are never all increased or diminished at the same
time; I except however the state of excitement at the commencement
of some fevers, when all are suppressed. In every other case, when
one fluid is abundantly poured out, the others are diminished; thus
the skin is dry in dropsies. There is sweating in the first stages of
phthisis pulmonalis; but when in the latter, dropsical effusions are
considerable, sweating ceases.
I have moreover divided into two classes the causes of increased
exhalations. 1st, One of these proves an increase of life; 2d, the
other, a real diminution of the vital forces; hence active and passive
exhalations. How can the same phenomenon arise from two causes exactly
opposite? It is difficult to determine precisely; but so many phenomena
prove this distinction of exhalations as well as secretions, that we
cannot refuse to admit it. It is important to recollect this in the
following article.